Gain controlled amplifier

Abstract

A gain controlled amplifier comprising a first means for providing a first current and a second current corresponding to an input signal, a second means for providing a first attenuated current corresponding to the first current, a third means for providing a second attenuated current corresponding to the second current, a fourth means for providing a control signal for changing magnitude of the first and second attenuated currents, and fifth means for providing an output signal corresponding to amplitudes of the first and second attenuator currents. The first means comprises a split current generator for separately providing the first current corresponding to the positive component of the input signal and the second current corresponding to the negative component of the input signal.

What is claimed is: 
     
       1. A gain controlled amplifier comprising: (a) first means for separately providing a first current corresponding to the positive component of an input signal and a second current corresponding to the negative component of said input signal;   (b) second means connected to said first means for providing a first attenuated current corresponding to said first current;   (c) third means connected to said first means for providing a second attenuated current corresponding to said second current;   (d) fourth means connected to said second and third means for providing a control signal for changing magnitude of said first and second attenuated currents;   (e) fifth means connected to said second and third means for providing an output signal corresponding to said first and second attenuated current;   (f) sixth means coupled to said first, second and third means, said sixth means being responsive to a third current which corresponds to a difference between said first current and said first attenuated current, and said sixth means also being responsive to a fourth current which corresponds to a difference between said second current and said second attenuated current, said sixth means providing said first means with an input current corresponding to said input signal.   
     
     
       2. A gain controlled amplifier of claim 1, wherein said sixth means includes: a first amplifier whose non-inverted input is connected to a ground circuit with zero voltage potential and whose inverted input is provided with said fourth current;   a first input impedance provided between said input signal and the inverted input of said first amplifier; and   a first current mirror circuit connected to said second means, for providing said third current to the inverted input of said first amplifier.   
     
     
       3. A gain controlled amplifier of claim 1, or 2, wherein said first means includes: a second amplifier whose non-inverted input is connected to a ground circuit with zero voltage potential;   a second input impedance provided between said input signal and the inverted input of said second amplifier;   a first transistor of a first conductivity type whose base and collector are connected to the inverted input of said second amplifier and whose emitter is connected to the output of said second amplifier so that the base-emitter path of said first transistor constitutes a negative feedback loop and the inverted input of said second amplifier is an imaginary ground; and   a second transistor of the first conductivity type for providing said first current, whose base and emitter are respectively connected to the base and emitter of said first transistor so that said first and second transistors constitute a second current mirror circuit, whereby   the magnitude of said first current is substantially zero and said first current causes no shot noise when the amplitude of said input signal is zero.   
     
     
       4. A gain controlled amplifier of claim 1, or 2, wherein said first means includes: a second amplifier whose non-inverted input is connected to a ground circuit with zero voltage potential;   a second input impedance provided between said input signal and the inverted input of said second amplifier; and   a third transistor of a first conductivity type for providing said second current, whose emitter is connected to the inverted input of said second amplifier and whose base is connected to the output of said second amplifier so that the base-emitter path of said third transistor constitutes a negative feedback loop and the inverted input of said second amplifier is an imaginary ground, whereby   the magnitude of said second current is substantially zero and said second current causes no shot noise when the amplitude of said input signal is zero.   
     
     
       5. A gain controlled amplifier of claim 1, or 2, wherein said first means includes: a second amplifier whose non-inverted input is connected to a ground circuit with zero voltage potential;   a second input impedance provided between said input signal and the inverted input of said second amplifier;   a first transistor of a first conductivity type whose base and collector are connected to the inverted input of said second amplifier and whose emitter is connected to the output of said second amplifier so that the base-emitter path of said first transistor constitutes a negative feedback loop and the inverted input of said second amplifier is an imaginary ground;   a second transistor of the first conductivity type for providing said first current, whose base and emitter are respectively connected to the base and emitter of said first transistor so that said first and second transistors constitute a second current mirror circuit; and   a third transistor of the first conductivity type for providing said second current, whose emitter is connected to the inverted input of said second amplifier and whose base is connected to the output of said second amplifier so that the base-emitter path of said third transistor constitutes a negative feedback loop and the inverted input of said second amplifier is an imaginary ground, whereby   the magnitude of said first and second currents is substantially zero and said first and second currents cause no shot noise when the amplitude of said input signal is zero.   
     
     
       6. A gain controlled amplifier of claim 1, or 2, wherein said fifth means includes: a third amplifier whose non-inverted input is provided with a given voltage potential, whose inverted input receives said first and second attenuated currents and whose output delivers said output signal; and   a feedback impedance connected between the inverted input and the output of said third amplifier.   
     
     
       7. A gain controlled amplifier of claim 1, or 2, wherein said third means includes a first differential transistors pair of a first conductivity type whose bases receive said control signal; and wherein said second means includes a second differential transistors pair of the first conductivity type whose bases receive said control signal; and a third current mirror circuit coupled with one collector circuit of said first differential transistors pair and one collector circuit of said second differential transistors pair, for changing the flow direction of said first attenuated current so that the phase of said first attenuated current is anti-phased from said second attenuated current, said third current mirror circuit including a second conductivity type transistors pair.   
     
     
       8. A gain control amplifier comprising: (a) a signal source means for providing a first signal corresponding to the positive component of an input signal and a second signal corresponding to the negative component of said input signal;   (b) an attenuator means connected to said signal source means for attenuating said first and second signals and providing a first and second attenuated signals in accordance with a control signal;   (c) a signal inverter means connected to said attenuator means, for inverting said first attenuated signal to an inverted signal; and   (d) a signal composing means connected to said attenuator means and said signal inverter means, for composing said second attenuated signal and said inverted signal to provide an output signal, wherein   a transfer function of the gain controlled amplifier is changed by said control signal.   
     
     
       9. A gain controlled amplifier of claim 8, further comprising: a signal converter means connected to said signal source means and said attenuator means, for converting said input signal to an input current and providing said input current to said signal source means, wherein   said signal converter means receives a third signal corresponding to a difference between said first signal and said first attenuated signal and a fourth signal corresponding to a difference between said second signal and said second attenuated signal.   
     
     
       10. A gain controlled amplifier of claim 8 or 9, wherein said attenuator means includes a differential transistors pair of which common emitters receive said first signal and one of which collector provides said first attenuated signal. 
     
     
       11. A gain controlled amplifier of claim 8 or 9, wherein said attenuator means includes a differential transistors pair of which common emitters receive said second signal and one of which provide said second attenuated signal.